There is a continued consumer demand for smaller and lighter portable electronic devices, such as, for example, mobile telephones, musical devices and players, personal digital assistants and the like to provide increasing numbers of different functionalities and features. In such portable handheld devices, it is an important design goal and consideration to provide a reduction in the size of the different component structural elements and a higher degree of feature integration. It is a further important design goal and consideration to provide a simplified input/output (I/O) interface that is usable and inter-exchangeable with different devices or units as well as to reduce feature implementation and operational manufacturing costs.
Possible sources for size and cost reduction are the traditional electronic circuits/chips that are used and which can be unproportionally expensive in low cost applications. Recently developed circuit technology based on circuits built-up by Organic Thin Film Transistors (OTFTs) structures rather than on traditional silicon (Si) semiconductor circuits are being looked to for such low cost applications. An OTFT typically has a Field Effect Transistor (FET) configuration, where the semiconducting material is an organic component or material such as polymeric, oligomeric, or molecular for example, and the Gate (G), Source (S), and Drain (D) electrodes may be made of various metals. However, the OTFT can also be manufactured with organic electrodes, such as, for example, various known conductive polymers, oligomerics, or molecular organic material. A schematic representation of a typical OTFT, in this case an organic field effect transistor (OFET) structure, is illustrated as a bottom-gate configuration in FIG. 1 and as a top-gate configuration in FIG. 2.
Presently, it is known to those skilled in the art to manufacture OTFTs on flexible substrates, using for example, vacuum deposition techniques at low temperatures or by various solution processing technologies. The OTFTs with the best performance are manufactured by vacuum evaporation/sublimation techniques and are usually based on small organic molecules, such as, Pentacene and oligothiophenes, and metal “electrodes” (i.e., G, S, and D). The performance (e.g., field-effect mobility, on/off-ratio, etc.) of these OTFTs can be even better than that for amorphous silicon, (a-Si) based devices. However, OTFTs can also be manufactured by various printing techniques also referred to as solution processing, using printed “electrodes” as well. The performance of a printed OTFT is usually not as good as the performance of a vacuum deposited OTFT. Nonetheless, the performance of a printed OTFT structure is more than adequate for low frequency applications. Furthermore, the charge carrier mobilities of solution processed OTFTs are approaching the maximum values achievable with vacuum evaporated OTFTs. In other words, if the printed organic circuits are used in low frequency applications such as input detection from a keyboard or output for controlling the illumination of a keyboard, the performance is more than adequate.
One technology used today to “print” OTFTs and organic circuits on substrates is based on ink-jet printing techniques and principles. The ink-jet printing technique provides a tool for depositing the various/multiple materials needed for organic circuits in an easily controlled process. One of the benefits of using a “printing” technique is the possible use of “reel-to-reel” (R2R) manufacturing processing to obtain circuits on a flexible or rigid substrate. Thus, the OTFTs are excellent candidates for simple and inexpensive mass manufacturing using R2R manufacturing processes. Ink-jet printing is one of the techniques that may be used in R2R manufacturing processes for printing flexible electronics such as, circuits, displays, and the like on various substrates. However, there is one drawback with the ink-jet printing of OTFT structures and circuits that is a result of the spreading of the ink-jet droplet when it hits the surface. Prior attempted solutions to this problem have been proposed including using various (physical) barriers to define or pre-pattern the area where the material is printed, or by surface treating the substrate, for example, by depositing a chemical barrier of some type as is known to those skilled in the art.
The barriers are usually made in a normal lithography process, i.e. deposition of resist, illumination through a mask, and the development of the illuminated pattern. This results in a “cavity” where the ink-jet droplet can spread evenly. The “chemical barrier” is made by surface treating the substrate into, for example, hydrophobic and hydrophilic areas, respectively (in the case of water soluble “ink”). The surface tension of the ink-jet droplet on the various regions will thus define the spreading of the droplet. The chemical treatment of the substrates is also often done in a “lithography” process.
The pre-patterning of a substrate using chemical barriers and the like as known to those skilled in the art for the depositing of organic materials on a substrate is an additional process that increases the cost of the technology used to apply the organic and inorganic material to the substrate surface. It would be desirable therefore to provide an alternate way or method to pre-define the area for receiving the organic material of the organic semiconductor device or organic circuit.
It would also be desirable to provide a method for simplifying the deposition of organic circuits on a substrate.
It is further desirable to provide a method for depositing organic or inorganic material on a suitable substrate for use in mass manufacturing of OTFT structures and circuits with R2R manufacturing processes.